A new study suggests drier weather will likely eliminate any advantage for Canada's boreal forest from higher temperatures caused by climate change.

Scientists had predicted that warmer conditions and a higher level of carbon dioxide, which plants breathe in, would promote growth.

And Martin Girardin of the Canadian Forest Service said some parts of the vast band of green that stretches across the northern provinces are expanding.

But his work published in the Proceedings of the National Academy of Sciences has found that enough forest stands are suffering under climate change to cancel out those benefits.

"There are some trends that are pretty obvious," Girardin said in an interview from Quebec City on Monday.

His study measured boreal forest growth over the last 60 years using decades of satellite imagery combined with tree-ring data from thousands of trees at hundreds of sites. Girardin wanted to see how climate change is affecting what is often called one of the largest undisturbed ecosystems left on Earth.

Temperatures at the study sites have already increased by between half a degree and three degrees.

"It could be expected that these changes should have led to increases in forest growth in this subcontinental region," says the report.

In some places, that's what seems to be happening.

"In British Columbia, there is an increase in forest growth," said Girardin. "It's pretty robust."

Pacific maritime forests have been growing about one per cent faster per year between 1982 and 2002, his analysis shows. Similar gains were seen in boreal stands north of the Great Lakes.

Everywhere else, however, the forest is expanding less.

Growth east of the Rocky Mountains, for example, has slowed by nearly a percentage point per year. So has growth in the Maritimes.

The limiting fact appears to be water, said Girardin.

"Trees are getting increasingly thirsty," he said. "As warming increases, there are no very large increases in precipitation. Warming may be favouring some aspects of growth, like the lengthening of the growing season, but during the summer there's a need for water and it seems there's not enough."

In the summer of 2015, Agriculture Canada figures show that the Northwest Territories and the northern reaches of the provinces received between 60 and 85 per cent of normal precipitation. Soil moisture was less than 40 per cent of normal.

Dry, warm years can impair growth through increased wildfires and insect infestations. Girardin also suspects nutrient-poor soils are preventing trees from taking advantage of higher carbon dioxide levels in the air.

The paper concludes that warmer temperatures have failed to increase growth in the boreal forest.

"Averaged across Canada's boreal forest, growth did not change significantly."

Girardin said calculations are vital in determining whether the boreal forest -- which covers northern countries around the world -- will continue to store carbon or begin releasing it. Those carbon stores are unimaginably huge -- about 14 per cent of all land plants in the world grow in boreal forests.

Changes in the forest create changes in the "services" it provides, he added, from clean water to nesting grounds for billions of songbirds. Some areas may become more difficult for the forestry industry.

"Our capacity for taking wood out of these forests in a sustainable way would be difficult in some areas."